1. Field of the Invention
This invention relates to improvements in standby time in a dual mode mobile communication device such as a mobile telephone or PDA with a cellular connection.
2. Description of the Related Art
Currently the most commonly used cellular communication network in most countries uses GSM technology to communicate. However, improvements in communication technology are being made and new communication formats are being produced. At least in the initial stages of rollout of a new format communication network, coverage will be patchy. Therefore, it is necessary for new handsets to be able to operate on at least the old network, e.g. GSM and new network, e.g., UMTS and to switch between the two for both monitoring the networks for quality of service and for receiving and making calls.
The trend has been to make smaller and smaller mobile communication devices such as mobile telephones. However, to be attractive to the public these devices require a significant standby time in order that they do not need to be recharged too frequently. Improvements in battery technology have enabled a reduction in size whilst at the same time permitting the standby time to be increased.
The major influences on standby time are battery size, the current which is drawn in receive mode when the device is monitoring the network for any incoming calls, and the time which is spent in receive mode.
A device which operates in a single network only has to monitor that network for incoming calls and does this periodically. However, a dual mode handset has to monitor two networks that use different access technologies (using two networks of the same technology is not a particular problem). Therefore, the time spent in receive mode will inevitably be higher than in a single network device. Typically, in a dual mode device, 40% of the standby current used is accounted for by leakages, 35% by monitoring the primary network, and 25% by monitoring the secondary network.